Superconducting electrical machines

ABSTRACT

A synchronous electrical generator having a rotor with a superconducting winding and coolant ducts for the winding and for the end part of the rotor, liquid helium being supplied to the winding coolant ducts through a radial passage and the heat generated by centrifugal action on the liquid passing through the passage being conducted back to the radially inner end of the passage and dissipated in the liquid cooling the end part of the rotor.

United States Patent 1 1 Ross [54] SUPERCONDUCTING ELECTRICAL MACHINES[75] Inventor: John Sterry Hawley Ross, Newcastle upon Tyne, England[73] Assignee: International Research & Development Company, Limited[22] Filed: Feb. 16, 1971 [21] Appl.No.: 115,653

[52] US. Cl ..310/52 [51] Int. Cl. ..H02k 9/00 [58] Field of Search ..3l0/55, 52, 40, 54, 310/56, 57, 58, 59, 61, 64, 265,10; 62/505,

[56] References Cited UNITED STATES PATENTS 3,517,231 6/1970 Massar..310/52 111 3,729,640 1451 Apr. 24, 1973 3,368,087 2/1968 Madsen.310/52 3,440,456 4 1969 Grunwald ..310/52 3,521,091 7 1970 Halas..310/52 3,478,232 11 1969 Eder ..310 40 2,986,905 6/1961 Kocher..62/475 Primary Examiner-R. Skudy AttorneyKemon, Palmer & Estabrook[57] ABSTRACT A synchronous electrical generator having a rotor with asuperconducting winding andcoolant ducts for the winding and for the endpart of the rotor, liquid helium being supplied to the winding coolantducts through a radial passage and the heat generated by centrifugalaction on the liquid passing through the passage being conducted back tothe radially inner end of the passage and dissipated in the liquidcooling the end part of the rotor.

5 Claims, 1 Drawing Figure SUPERCONDUCTING ELECTRICAL MACHINES Thisinvention relates to superconducting electrical machines.

In the co-pending U.S. Pat. Application Ser. No. 43693 filed June 5,1970 now U.'S. Pat. No. 3,648,082 there is described a synchronouselectrical machine in which the rotor carries a superconducting fieldwinding which is supplied with do. excitation. The stator winding isnon-superconducting and constitutes the armature winding. Cryogenicfluid such as liquid helium is used to reduce the temperature of therotor winding to temperatures at which the rotor winding becomessuperconducting, usually temperatures of the order of 5 K. Such fluidcan be produced in a refrigerator outside the machine or part of therefrigerating equipment such as turbo-expanders may be located withinthe rotor so as to rotate therewith. In the latter case the equipment ispreferably located coaxial with the rotor axis to minimize centrifugaland gyroscopic forces. Cryogenic fluid can also be used to cool axiallyouter parts of the rotor body to produce a thermal resistance betweenthe winding and the rotor shaft to restrict ingress of heat along theshaft into the winding.

If the path for cryogenic fluid to the rotor winding is radiallyoutwards as it will be in most instances especially when therefrigerating equipment is located around the axis of the machine, thereis an increase in pressure in the fluid as it passes to the winding andthis results in a heating up of the fluid. A heating up of the fluid ofone or two degrees can be serious because of the increased amount ofrefrigeration work required.

In accordance with the present invention there is provided asuperconducting electrical machine com-' prising a hollow rotor having acentral part and two end parts joining the central part to rotor shaftswhich are supported in bearings, a superconducting winding arried by thecentral part of the rotor, winding cooiing ducts for circulatingcryogenic fluid to cool the winding, wall cooling ducts for circulatingcryogenic fluid to cool the wall of one end part of the rotor, supplymeans for supplying cryogenic fluid, a first passage extending generallyradially from the supply means to the winding cooling ducts, a secondpassage extending from the supply means to the wall cooling ducts, andheat transfer means for conveying heat from the radially outer end ofthe first passage to the supply means to dissipate this heat incryogenic fluid fed to the second passage.

When the first and second passages have a common junction with thesupply means, the heat transfer means extends from the radially outerend of the first passage to the said junction.

The heat transfer means is preferably a solid member of high thermalconductivity.

The invention will be described in more detail with the aid of anexample illustrated in the accompanying drawing, which is 'alongitudinal section of part of the rotor of a synchronous generator inaccordance with the present invention.

The rotor comprises a body or central part carrying a rotor winding 11of superconducting material such as niobium-titanium alloy. The rotorfurther comprises a rotor shaft 10a joined to one end of the centralpart 10 by a hollow end part 10b of conical form. The .rotor shaft 10aand a similar shaft (not shown) at the other end of the rotor aremounted in bearings l2.

Coolant ducts 13 are associated with the winding 11 and are suppliedwith cryogenic fluid, such as liquid helium, through a radial passage14. The end part 10b of the rotor is also provided with coolant ducts 15to minimize the inflow of heat to the winding along the wall of the endpart 10b. The coolant ducts 15 are supplied with cryogenic fluid througha passage 16 which also extends generally radially of the rotor. Theinner ends of the passages 14 and 16 have a common junction 17 with asource 18 of cryogenic fluid which comprises refrigeration equipmentmounted about the axis of the rotor and connected by a conduit 19 tofurther refrigeration equipment outside the rotor. For details of theconstruction and arrangement of the cryogenic source-18, which is onlyshown diagrammatically in the drawing, reference is made to theabove-mentioned copending application, which also shows constructionaldetails of other parts of the present machine.

In an alternative construction the refrigeration equipment is mountedwholly outside the rotor and cryogenic fluid is fed to the interior ofthe rotor by the conduit 19. In either case liquid helium is supplied tothe junction 17 of the passages 14 and 16 at a temperature of about 5 K.The major portion of the liquid flows along the passage 16 to thecoolant ducts 15. Liquid entering the passage 14 flows radially outwardsto the coolant ducts 13 in the winding 11 and its pressure is increasedby the action of centrifugal forces due to the rotation of the rotor.

As a result, the liquid heats up by two or three degrees and this isundesirable because the winding is raised above its operatingtemperature. To counteract the heating effect, heat transfer means areprovided in the form of a solid member 20 of high thermal conductivitymaterial such as aluminum or copper which extends from the outer end ofthe passage 14 to the inner end and thus conducts heat back to thejunction 17. This heat is dissipated in the much larger quantity ofliquid being fed from the junction 17 through the passage 16 to thecoolant ducts l5 and results in a much lower temperature increase inthis liquid. The temperature of the liquid in the ducts 15 is in anycase less critical since it serves solely to cool the end part1 0b ofthe rotor and thus provide a thermal resistance between the winding andthe rotor shaft to restrict inflow of heat to the winding.

The arrangement shown can, if necessary, be duplicated at the other endof the rotor and at each end there can be more than one of the passages14 and 16 with the associated heat transfer member 20.

By using the end part 10b as a thermal resistance the bearing 12 canoperate at normal ambient temperature, for example 300 K.

What is claimed is:

1. In a superconducting electrical machine, a hollow rotor having acylindrical center part, two conical end parts, and rotor shafts jointedto said central part by said end parts, bearings supporting said rotorshafts, a superconducting winding carried by said central part of therotor, winding cooling ducts in heat exchange relation with said windingfor circulating cryogenic fluid to cool said winding, wall cooling ductsin heat exchange relation to one of said conical end parts forcirculating cryogenic fluid to cool the wall of one end part of therotor, supply means for supplying cryogenic fluid, a first passageextending generally radially from said supply means and said heattransfer means extends between this common junction and said radiallyouter end of the first passage.

4. A machine as claimed in claim 3 in which said heat transfer meanscomprise a solid member of high thermal conductivity.

5. A machine as claimed in claim 1, wherein the said supply meansincludes refrigeration equipment located within the rotor.

1. In a superconducting electrical machine, a hollow rotor having acylindrical center part, two conical end parts, and rotor shafts jointedto said central part by said end parts, bearings supporting said rotorshafts, a superconducting winding carried by said central part of therotor, winding cooling ducts in heat exchange relation with said windingfor circulating cryogenic fluid to cool said winding, wall cooling ductsin heat exchange relation to one of said conical end parts forcirculating cryogenic fluid to cool the wall of one end part of therotor, supply means for supplying cryogenic fluid, a first passageextending generally radially from said supply means to said windingcooling ducts, a secoNd passage extending from said supply means to saidwall cooling ducts, and heat transfer means for conveying heat from theradially outer end of said first passage to said supply means todissipate heat from said windings in cryogenic fluid fed to said secondpassage.
 2. A machine as claimed in claim 1 in which said heat transfermeans comprise a solid member of high thermal conductivity.
 3. A machineas claimed in claim 1, wherein said first and second passages have acommon junction with said supply means and said heat transfer meansextends between this common junction and said radially outer end of thefirst passage.
 4. A machine as claimed in claim 3 in which said heattransfer means comprise a solid member of high thermal conductivity. 5.A machine as claimed in claim 1, wherein the said supply means includesrefrigeration equipment located within the rotor.